Review multi fixes in weyou's fork

[bovine]

@weyou made some fixes to multi curl handling that might be useful to incorporate back into this repo.

It looks like there were also some Windows-specific fixes also, which may or may not still be necessary after the recent work by apnadkarni.

master...weyou:master

[wrenashe]

Yes, please.

[bovine]

Yes, please.

Is there anything specific that you are aware of in that fork that would be important? Would you be able to help identify those things?

[wrenashe]

Without that fix, TclCurl does not work with the later Curl lib version, like 7.72.0. And it looks not Windows only, I tried Linux, TclCurl does not work either without that patch.